A. Field of the Invention
The invention relates to a preventive maintenance of etching equipment for the semiconductor technology. More particularly, the invention relates to a method for removing polymer stacked on a lower electrode within an etching reaction chamber.
B. Description of the Related Art
Along with progress of the fine processing technology, the degree of integration and the performance of semiconductor devices is gradually increasing. In the semiconductor manufacturing process, the primary function of the etching process is to remove layers on which there are no photoresist layers in the photolithography process, such that the mask patterns are transferred to the layers. In the above-mentioned etching process, there are two main methods: (1) the process of wet etching performed by a chemical reaction and (2) the process of dry etching performed by physical mechanisms. Compared with the process of wet etching, the process of dry etching takes a more important part in the fine processing technology due to anisotropic properties. In the physical mechanism of the process of dry etching, plasma is utilized to dissociate molecules of a reaction gas to reactive ions, and then the layers made of materials such as SiO2, Si3N4, poly-Si, or Al alloy are removed by the bombardment of the reactive ions.
FIG. 1 is cross-sectional view showing the structure of etching equipment for performing the process of dry etching. Referring to FIG. 1, etching equipment 1 for performing the process of dry etching consists of an upper electrode 10, a lower electrode 20, a radio frequency generator 30, and a reaction chamber 70. In general, the upper electrode 10 is connected to the wall 40 of the reaction chamber 70, and both are grounded. In addition, the radio frequency generator 30 is connected to the lower electrode 20, and a wafer 50 to be etched is placed on the lower electrode 20. Referring to FIG. 2, the wafer 50 includes a substrate 51 on which a conductive, semiconductive, or insulating layer 52 is formed. A patterned photoresist layer 53 has been provided on the surface of the layer 52 by the process of photolithography before the wafer 50 is transferred into the reaction chamber 70. During the process of dry etching, a reaction gas (not shown) for carrying out dry etching is supplied into the reaction chamber 70 through a supply tube 60, and then is dissociated into ions by the radio frequency generator 30 to form a plasma. After the formation of the plasma within the reaction chamber 70, the plasma ions are accelerated by the electric potential difference between the upper electrode 10 and lower electrode 20 so as to bombard the exposed part 54 of the layer 52 formed on the surface of the substrate 51. Afterwards, the reaction product, as a result of the bombardment, is expelled through an exhaust tube 80 by a vacuum system (not shown) connected to the exhaust tube 80. Therefore, the transfer of the pattern from the photoresist layer 53 to the layer 52 is achieved.
In the manufacturing process of semiconductor devices, a layer made of silicon dioxide is usually applied as the insulating layer to be etched and the reaction gas for carrying out dry etching usually contains carbon and fluorine atoms. As a result, a polymer (not shown) including carbon and fluorine is produced by the chemical reaction between the reactive ions dissociated from the reaction gas and the silicon dioxide of the insulating layer. A part of the polymer stacks on the wall 40 of the reaction chamber 70 and the peripheral surface 90 of the lower electrode 20. After a period of time, the stacked polymer becomes the source of particle contamination and affects the yield of the wafer 50. In order to prevent the polymer from being stacked on the lower electrode 20 so as to make the process of dry etching effective, it is necessary to perform preventive maintenance of the reaction chamber 70 during intervals.
FIG. 3 is a plane view showing the structure of the lower electrode 20. Referring to FIG. 2, the polymer 100 adheres to the peripheral surface 90 of the lower electrode 20 in the form of a lump. The conventional preventive maintenance of the lower electrode 20 is to remove the polymer 100 adhering to the surface by the process of wet cleaning as described in the following.
At the beginning of the conventional preventive maintenance, the temperature of the lower electrode 20 is set to a room temperature. Then, the reaction chamber 70 is repeatedly cleaned several times by a pump/purge cleaning method. Next, the reaction chamber 70 is opened after the internal pressure of the reaction chamber 70 is up to atmospheric pressure by supplying nitrogen gas through the supply tube 60. Afterwards, using Cleaner 5060 (having as a main component C6F14), produced by the 3M corporation, as a cleaning solution, the surface of the lower electrode 20 is wiped several times. Furthermore, using a scraper (not shown), the polymer 100 adhering to the peripheral surface 90 of the lower electrode 20 is removed. Finally, the surface of the lower electrode 20 is wiped several times again by using Cleaner 5060 produced by the 3M corporation.
According to practical operations of the conventional preventive maintenance, it is necessary to use a large amount of Cleaner 5060 because the conventional method is not effective to remove the polymer 100 adhering to the peripheral surface 90 of the lower electrode 20. Moreover, it takes a long time to finish the conventional preventive maintenance due to the use of the scraper. The scraper also makes the surface of the lower electrode 20 worn and damaged resulting in a shortening of its lifespan, and therefore affects the stability of the etching process.
In view of the above problems and disadvantages, it is therefore an object of the invention to provide a method for removing polymer stacked on a lower electrode within an etching reaction chamber without the use of an additional cleaning solution or scraper.
The invention is an improvement over the conventional preventive maintenance of a lower electrode. Using the invention, the polymer stacked on the lower electrode is effectively removed, the cleaning time is shortened, the quantity of the required cleaning solution is decreased, and the lifespan of the lower electrode is increased.
According to the invention, a method for removing polymer stacked on a lower electrode within an etching reaction chamber comprises the following steps: setting a first temperature of the lower electrode in the range from xe2x88x9210xc2x0 C. to 0xc2x0 C., preferably 0xc2x0 C.; cleaning the reaction chamber 5 to 50 times, preferably 20 times, by a pump/purge cleaning method; supplying at least one gas selected from a group consisting of nitrogen and an inert gas into the reaction chamber such that the internal pressure is equal to atmospheric pressure; opening the reaction chamber; keeping the reaction chamber open and the temperature of the lower electrode at 0xc2x0 C. for 5 to 15 minutes, preferably 10 minutes; wiping the surface of the lower electrode with a piece of clean cloth; setting a second temperature of the lower electrode in the range from 20 to 30xc2x0 C., preferably 25xc2x0 C.; and wiping the surface of the lower electrode several times by using at least one cleaning solution selected from a group consisting of de-ionized water, isopropanol (IPA), ethanol, a solution of hydrogen peroxide in water, and Cleaner 5060 (having as a main component C6F14) produced by the 3M corporation.